There has been known an air cleaning apparatus such as a mask including a filtering portion, as a constitutional element, that filters air contaminated or polluted with a poisonous gas, wherein the filtering portion removes the poisonous gas to clean the air. Also, there has been known a gas mask, which is one of air cleaning apparatuses that detects the concentration of a poisonous gas included in the air after passing through the filtering portion by a sensor provided on a downstream side of the filtering portion in the gas mask. There has been known an air cleaning apparatus that can estimate a residual breakthrough time of the filtering portion by estimating a degree of breakthrough progress of a filtering member of the filtering portion. Further, there has been known an air cleaning apparatus that is capable of predicting a life span of the filtering portion in accordance with variation in a flow rate of air contaminated with a poisonous gas passing through the filtering portion or variation in humidity of the air.
For example, a protective mask described in JP 2006-263238A (PTL 1) includes a semiconductor odor sensor that can estimate a time of replacement for a canister, disposed on the downstream side of the canister.
In a filtering replacement time discriminating apparatus described in JP 1991-207425A (PTL 2), a first gas sensor is provided on the upstream side of a filter so as to measure a concentration of molecule of unnecessary gases such as a gas having an offensive odor in the outside air. A second gas sensor and an anemometer are provided on the downstream side of the filter. A difference between the molecular concentration of the unnecessary gas C1 detected by the first gas sensor and the molecular concentration of the unnecessary gas C2 detected by the second gas sensor is calculated, and an amount of airflow Q per unit time to be processed through the filter is calculated using the anemometer as well. An amount of removal of the unnecessary gas through the filter is calculated based on C1, C2, and Q, and a judgment is made by comparing the amount of removal with a limit removal offensive gas amount at which the filter deteriorates, so that it can be determined whether the breakthrough time is left.
Also, an air cleaning apparatus described in JP 2007-117859A (PTL 3) includes a flow rate detector to detect a flow rate of air passing through a gas filter and a humidity detector to detect the humidity of the air passing through the gas filter, calculates an amount of exhaustion of the gas filter based on the detected data from each detector, and predicts a residual amount of the gas filter based on the amount of exhaustion. The residual amount of the gas filter indicates the residual amount of the breakthrough time of the filtering member.